The invention relates to those apparatuses which in the tire industry are used to test the behaviour of the rubber compounds, in connection with their rolling on surfaces with different morphological characteristics.
The apparatuses considered in the present description essentially consist of a so-called xe2x80x9croad drumxe2x80x9d, namely a motorised cylindrical drum with a diameter of the order of 70-100 cm, on which a roller of smaller dimensions (generally with a diameter not greater than ⅕th of the road drum) constituting the specimen and having a radially external portion that over a thickness of preferably not less than 2 mm, is made with the vulcanized compound to be examined.
Also the specimen is driven and causing it to roll about the road drum, it is possible to analyse the behaviour of the compound being examined according to different operating situations which can be simulated with the apparatus, for example with relative slipping and/or with set drift angles.
In this manner it may be studied the behaviour of a compound under conditions of pure rolling contact between road drum and specimen or when there is relative slipping between them or when the inclination of the specimen with respect to the road drum is such as to reproduce the conditions to which the compound of a tire tread is subject during bends.
Furthermore, in some more complex machines, the tests may be performed by spraying water, dust and/or other elements in the zone where there is contact between the drum and specimen, thus fully simulating those situations which may occur in reality.
The present invention is based on the Applicant""s realisation that, precisely in such a context, the apparatuses known hitherto are not satisfactory.
Indeed, it must be taken into account that the roller which forms the specimen to be tested is usually mounted on the end of a spindle rotating about an axis parallel to that of the road drum.
This spindle is operated in a manner known per se, at the opposite side with respect to the specimen; however, in order to operate it in an environment which is exposed to water or the other elements mentioned above, some precautions are required: the latter include the use of sealed bearings.
These bearings, however, produce an inevitable friction which is opposite to the rotation of the spindle, thereby altering significantly the measurements performed; this is the case in particular of the evaluation of the torques acting with respect to the axis of rotation of the spindle.
The object of the present invention is therefore that of providing an apparatus for testing rubber-compound specimens of tires, having structural and operational characteristics such as to overcome the drawbacks mentioned.
According to a first aspect, the invention relates to an apparatus for testing tire compounds, comprising a road drum and a specimen rotating about respective parallel axes and in rolling contact with each other, driving means for rotation of the road drum and the specimen, characterized in that these means comprise a specimen driving group in which there is a spindle driven by a motor, wherein the spindle is rotatably housed in a casing and the motor is fixed in a cradle seat integral with the casing so as to form a rigid body therewith, this body being supported in an idle manner with respect to the axis of rotation of the specimen.
Further characterising features of such an apparatus are set out in the claims which will follow.